The butterscotch wasn't the right choice. It is sweet, creamy and buttery, but not a flavor that's in Killa Vanilla (maybe a drop or 2 to accentuate, but certainly not one of the main flavors).
Maybe you're satisfied with the butterscotch... if not (TPA butterscotch never did much for me) then check out the Nature's Flavors BS. It's excellent. You have to buy an ounce of it from them, but Vaperite sells some of their flavors in 6ml sizes. Unfortunately, VR seems to be out of BS right now. Hopefully they'll get it back soon.
I doubt it will get you any closer to KV, but if you like BS, it's one to add to the list of things to try IMO.